1. Field of the Invention
The present invention relates to a transmission shift position sensor and more particularly to a transmission shift position sensor configured to be disposed within an automatic transmission housing and directly coupled to a so-called rooster comb. The transmission shift position sensor includes a rotary position sensor, optionally configured to be electronically calibrated to the detent positions of the rooster comb, to compensate for mechanical tolerances in the assembly and generate an electrical signal, for example, a linear signal pulse width modulated signal, representative of the position of the transmission shift position.
2. Description of the Prior Art
Various transmission shift position sensors for sensing the position of a transmission shifter assembly or an automatic transmission are known in the art. Examples of such shift position sensors are disclosed in U.S. Pat. Nos. 4,683,768; 4,907,475; 4,936,166; 5,247,279; 5,468,197; 5,651,293; 5,673,596; 5,775,166; 5,846,160; 5,847,344; 5,867,092; 5,934,436; 6,018,294; 6,027,026; 6,072,390; 6,124,789 and 6,209,408. These patents disclose various techniques for sensing the position of the transmission shift used to shift gears of an automatic transmission. For example, U.S. Pat. Nos. 5,847,344; 6,027,426 and 6,209,408 disclose transmission shift position sensors which sense the position of the transmission shift lever within the passenger compartment of the vehicle. However, the signals from such transmission shift position sensors are known to be not inherently accurate due to the tolerances in the mechanical linkages between the transmission shift lever and the automatic transmission. In particular, such automatic transmissions are hydraulic mechanisms which rely primarily on the position of manual control valves within the automatic transmission housings to direct fluid flow to change the shift positions, for example, as disclosed in U.S. Pat. Nos. 4,683,768; 4,936,166; 5,651,293 and 5,846,160, all hereby incorporated by reference. In general mechanical linkages are used to position hydraulic control valves which, in turn, control the automatic transmission. In general, these mechanisms include a so-called xe2x80x9crooster combxe2x80x9d that is mechanically coupled on one end to a transmission shift lever within the vehicle passenger compartment and is mechanically coupled to the hydraulic control valves within the automatic transmission housing. Such rooster combs are normally disposed within the automatic transmission housing and are formed with a cam surface having a number of detent positions which cooperate with a biasing member for latching each of the shift positions of the automatic transmission. Often times, tolerances or play in the mechanical linkages can result in relatively inaccurate signals being generated by transmission shift position sensors which rely on the position of the transmission shift lever within the vehicle passenger compartment such as disclosed in U.S. Pat. Nos. 5,847,344; 6,027,426 and 6,209,408. Such inaccurate transmission shift position sensor signals are highly undesirable for several reasons. First, such signals are known to be applied to a powertrain control module which prevents cranking of the engine unless the transmission is in the park or neutral positions. In addition, such position signals are also used to provide the vehicle operator with a visual indication of the shift position of the automatic transmission. Lastly, such signals are used to control operation of the reverse back-up lamps in an automobile. Accordingly, it is necessary to have a relatively accurate indication of the transmission shift position.
In an effort to improve the accuracy of such transmission shift position sensors, new sensors have been developed. For example, U.S. Pat. No. 4,907,475 discloses a shift position sensor which relies on pressure switches within the automatic transmission housing. With this sensor, the pressure at various points within the automatic transmission is sensed to provide a signal representative of the shift position of the automatic transmission. Such sensors are also subject to various inaccuracies which can result in an incorrect indication of the shift position of the automatic transmission. For example, such sensors are subject to changes in pressure within the automatic transmission; as well as tolerances in drifting of the set point of the pressure switches.
Still other systems have been developed which incorporate sensors within the transmission housing in an attempt to provide more accurate sensing of the position of the transmission shift lever. For example, U.S. Pat. No. 6,018,294 discloses a shift position sensor which includes a rooster comb which includes a cam surface which corresponds to the detent positions of the rooster comb. An electronic contact-type switch rides along the cam surface to provide an indication of the rooster comb and thus the shift position of the automatic transmission. Such a sensor as disclosed in the ""294 patent, incorporates a contact-type switch, which, unfortunately, is subject to wear and failure. Moreover, replacement of the worn switch would be rather difficult and expensive for a consumer since the switch is disposed within the transmission housing.
In order to avoid the problems associated with contact-type switches, sensors have been developed which incorporate non contact-type sensors. For example, U.S. Pat. No. 5,867,092 discloses a position sensor for a transfer case for a four wheel drive vehicle. The transfer case includes an input shaft which drives a planetary gear assembly which provides various speed reduction ratios to provide two-wheel or four-wheel operation. Various gear reduction ratios are selected by a shift control rod.
This includes a plurality of Hall effect sensors disposed within the transfer case housing. The Hall effect sensors are disposed to detect the position of a metal plate coupled to a transmission shift control rod. While the shift position sensor utilizes non-contact Hall effect sensors for sensing the position of a shift control rod in a transfer case, the sensor disclosed in the ""092 patent is based upon utilizing three Hall effect sensors and a metal plate attached to the shift control rod within the transfer case housing. Unfortunately, there is insufficient room in automatic transmission housing for such a configuration. Thus, there is a need for a non-contact sensor for sensing the position of a transmission shift lever which provides an accurate indication of the position of the transmission shift lever.
Briefly, the present invention relates to a transmission shift position sensor that is adapted to provide an indication of the position of a transmission shift lever. The transmission shift position sensor includes a rotary position sensor and a rooster comb formed as an assembly. The direct coupling of the sensor to the rooster comb provides a positive indication of the automatic transmission shift sensor without the need for compensating for tolerances in mechanical linkages.